This invention relates to a filter assembly for use as a filter insert in a boiler filter housing, particularly for purifying exhaust (waste) gases of nuclear installations. The filter insert is of the type which has a frame having the shape of a circular cylinder provided with a central inlet opening at its underside and containing individual filter elements which are distributed over the external circumference of the frame and through which fluid may pass from the inside outwardly. The intermediate spaces between the filter elements are bridged by sheet metal spacer/holder members and the filter elements are seated in a sealed manner relative to the cylindrical frame.
For purifying exhaust gases, particularly those generated in nuclear installations such as reprocessing installations for nuclear fuels, by separating suspended materials therefrom, filter inserts of the Special Stage S are necessary. The filter inserts have to be structured such that dependent upon the activity inventory of the utilized filter inserts, that is, dependent upon the purpose of use, the replacement of the filter insert can be performed either manually with the aid of the plastic bag technique or by remote control. The seal of the filter seat between the air to be filtered (raw air) and the filtered air (purified air) is, as a rule, monitored during operation.
For use with a remote servicing there have been utilized rectangular filters secured by screws to a five-sided frame and individually sealed for obtaining a quasi-circular filter insert. The five-sided frame is a welded construction. To five webs which form the frame for the rectangular filter inserts there are welded in a gastight manner the lid and the bottom of the circular filter insert. The filter bottom is provided with a gas inlet opening. In the quasi-circular filters which are formed of a plurality of rectangular filter inserts secured to the filter frame and sealed all around, the sealing properties of the annular, all-around seal which may have a length of several meters, cannot be verified. The welded seams of the filter insert also have a length of several meters.